There were over 8 million cancer-related deaths worldwide in 2013. According to the World Health Organization, this death toll will reach 13.1 million by 2030 unless rapid and cost- effective diagnostic technologies are developed for the early detection of the disease. Current diagnostic techniques such as ELISA are time-consuming for point-of-care settings and often cost-prohibitive for developing countries where resources are scarce. Here, we propose a potentially transformative all-carbon electronic biosensor based on a tube-in-a-tube semiconductor (Tube^2) created by our research team. A Tube^2 is composed of an atom-thick semiconductor nested within a charged, covalent functional shell. We hypothesize that conductance through the semiconductor can be completely controlled solely by surface functional groups on the shell such that binding of a small number of targeted cancer markers can be detected electrically. Our preliminary studies have shown evidence of chemically gated field effect detection of DNA using thin-film Tube^2 sensors. The proposed research will focus on three specific aims: 1) establishing the fundamentals of electrode-free chemical gating of Tube^2; 2) coaxial chemical lithography with light; and 3) label-free and multiplexed detection of cancer biomarkers by Tube^2 sensors. In Aim 1, a series of aryl functional groups will be attached covalently at controlled densities on Tube^2 to quantitatively determine the gating effects of surface functional groups. In Aim 2, we will investigate light-driven defunctionalization and re-functionalization of Tube^2 as the basis for a straightforward, fundamentally new fabrication approach to electronic sensor arrays. In Aim 3, chemically gated field effect detection of model cancer markers, including prostate-specific antigen and ?-fetoprotein, will be investigated in thin-film Tube^2 sensor arrays. This work may provide a new foundation for the development of rapid and cost-effective medical diagnostic technologies.